This invention relates to an anticorrosive cathodic electrodeposition paint to be applied on, for example, cold rolled steel sheets having no surface treatment.
Electrodeposition paints have an excellent throwing power and can form a protective film of uniform thickness on metallic substrates to protect the substrates from corrosion. For this reason the paints are extensively used in the automobile industry as a primer coating of bodies and other parts. The paint may exhibit a satisfactory anticorrosive effect when the substrate is subjected to a surface treatment such as zinc phosphate treatment before electrodeposition coating. However, when the substrate does not receive a satisfactory surface treatment, the paint will show only a poor anticorrosive effect unless a lead-containing anticorrosive pigment such as basic lead silicate is added to the paint. Because the use of lead pigments should be avoided or reduced for ecological reasons, attempts have been made to replace the lead pigments with other anticorrosive pigments such as phosphate pigments, molybdate pigments, borate pigments and the like. Similar attempts have been made to use ferric oxide (JP-A-02279773), bismuth hydroxide/tin, cerium hydroxide/tin, nickel hydroxide/tin (JP-A-05140487), bismuth/tin (JP-A-05247385), copper, nickel, zinc, cobalt, chromium, aluminum, manganese, zirconium, tin and iron (JP-A-04325572). However, none of the above attemps have been proven successful to impart cathodic electrodeposition paints with anticorrosive properties comparable to lead pigments.
Therefore, a need exists for a cathodic electrodeposition paint which eliminates or reduces the use of a lead pigment but has a satisfactory anticorrosive property comparable to or even better than the paint containing the lead pigment when applied on, for example, untreated cold rolled steel sheets.